1. Field of the Invention
The present invention relates to an abrasive pad and its manufacturing method as well as to a substrate, a wafer for example, polishing method using the said abrasive pad.
2. Description of the Related Art
Although it is usually desirable from the viewpoint of design that a semiconductor device be as fine as possible, the demand on the depth of focus in lithography step becomes severe. To solve this problem, the resist needs to be improved, which is however difficult. In view of this fact, some methods have been attempted so as to reduce the height differences in device structure. The height differences in device structure cause the difficulty of depth of focus. As one of these methods, in general, height differences in device structure are reduced by chemical mechanical polishing that utilizes a silicon wafer mirror-polishing technique.
The above chemical mechanical polishing will be described below with reference to FIG. 1 which schematically shows the configuration of a chemical mechanical polishing apparatus 10. The chemical mechanical polishing apparatus 10 has a polishing surface table 12 on which an abrasive pad 11 is mounted, a dresser 13, a carrier 14 for holding a wafer 20, and an abrasive slurry supply mechanism 15. Usually, the abrasive pad 11 has a disk-like shape. The polishing surface table 12, which has a short-cylinder-like shape, is rotated while being supported by a polishing surface table rotating shaft 12a. Diamonds 13a are electro-deposited on a metal plate of the dresser 13. The carrier 14 that holds the wafer 20 is supported by a carrier rotating shaft 14a and rotated independently of the polishing surface table 12 or following it. Further, the carrier 14 is equipped with a polishing pressure adjusting mechanism 14b. The carrier 14 is thus swung while being pressed against the abrasive pad 11 via the wafer 20. The abrasive slurry supply mechanism 15 supplies abrasive slurry to the surface of the abrasive pad 11 from a supply nozzle 15a.
A method for polishing the wafer 20 by using the chemical mechanical polishing apparatus 10 will be described below. First, the polishing surface table 12 is rotated by the polishing surface table rotating shaft 12a. At this time, since the abrasive pad 11 and the diamonds 13a are in contact with each other, the diamonds 13a scrub the surface of the abrasive pad 11 and dress it as the polishing surface table 12 is rotated. The dressing produces innumerable scratches on the surface of the abrasive pad 11. Usually, those portions of the abrasive pad 11 which have been split finely by the scratches are called a dressed layer, and the tips of the split portions are called hair tips of the dressed layer.
When abrasive slurry is supplied from the supply nozzle 15a to the surface of the abrasive pad 11 that is formed with the dressed layer, the abrasive slurry stays between the hair tips of the dressed layer. In this state, the carrier 14 that holds the wafer 20 is lowered to approach the abrasive pad 11 while being supported by the carrier rotating shaft 14a until the wafer 20 is brought into contact with the abrasive slurry that is provided on the abrasive pad 11. Then, the carrier 14 is swung while being pressed against the abrasive pad 11 via the wafer 20 by the polishing pressure adjusting mechanism 14b, whereby the wafer 20 slides on and is polished by the abrasive slurry that is provided on the abrasive pad 11.
However, in the above-described chemical mechanical polishing method, dressing shavings of the abrasive pad 11, diamonds that have dropped from the dresser 13, fragments produced by polishing of the wafer 20 or insulative film, spent abrasive slurry, and like impurities stick to the wafer 20 that is located on the abrasive pad 11 and cause microscratches, which will influence following steps, for example lithography step.
The sticking of those impurities to the wafer 20 is prevented by causing the abrasive slurry to spread to the entire surface to be polished of the wafer 20 and to capture the impurities, and then discharging the abrasive slurry from the abrasive pad 11. In addition, by causing the abrasive slurry to spread to the entire surface to be polished of the wafer 20, insufficiently polished portions are prevented from occurring in the surface to be polished, whereby the polishing rate is made uniform in that surface.
However, the supply of a large amount of slurry is not preferable in terms of cost. And there is another problem that as long as the abrasive pad is dressed, costs are required for repair, maintenance, etc. of the dresser.